Three independent studies published in the 22 December issue of Science reported that chromosome 10 probably harbors one or more genes that confer an increased susceptibility to late-onset Alzheimer's disease. The specific gene or genes have not yet been identified, but the fact that three separate studies employing different methods and datasets make it more likely that the linkage is not an experimental artifact.
A team led by Alison Goate at Washington University, St Louis, screened the entire genome of over 430 sibling pairs with Alzheimer's and identified a susceptibility locus on chromosome 10. "Two things about this new risk factor seem very significant," says Goate. "First, it appears to have as big an effect on risk as ApoE4 in our sample. Secondly, it has that effect independent of ApoE4," the only gene so far confirmed to be a risk factor for late-onset AD. A second paper by Steven Younkin and colleagues at Mayo Clinic, Jacksonville, Florida, mapped a gene that modifies plasma concentrations of Aβ-peptide to exactly the same region of chromosome 10. Plasma Aβ levels are altered in inherited forms of early onset AD. In the third Science paper, Rudolph Tanzi and colleagues at Massachusetts General Hospital report a linkage also to chromosome 10, albeit not to the same exact locus. "The region Tanzi's group identified is not in exactly the same place as the other two studies, but the linkage approach does not give precise localisation so we could be detecting the effects of the same gene", says Goate. The Tanzi group focused on chromosome 10 because it contains the gene for insulin degrading enzyme (IDE), a protein that is thought to degrade β-amyloid in the brain, and is considered a candidate gene for a risk factor for AD.—Hakon Heimer
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